The present invention relates to novel organosilicone polymers and their use in the manufacture of urethane cellular products, particularly flame-retarded flexible polyether polyol-based urethane foams.
It is well known that the urethane linkages of urethane foams are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure of the foam is provided by gas evolution and expansion during the urethane-forming reaction. In accordance with the "one-shot process" which is the most widely used industrial technique, direct reaction is effected between all of the raw materials which include the polyisocyanate, the active hydrogen-containing compound, the catalyst system, blowing agent and surfactant. A major function of the surfactant is to stabilize the urethane foam, that is, prevent collapse of the foam until the foamed product has developed sufficient gel strength to become self-supporting.
It is also well known that suitable active hydrogen-containing compounds include polyether polyols and polyester polyols. From the standpoint of their chemical structure, therefore, urethanes are usually classified as polyether and polyester urethanes, respectively. Urethane foams also differ with respect to their physical structure and, from this standpoint, are generally classified as flexible, semiflexible or rigid foams.
Although certain techniques of urethane manufacture such as the "one-shot process" and certain components of the foam formulation such as the polyisocyanates, amine catalyst and blowing agent, are generally useful, a specific problem associated with the production of a particular type of urethane foam and the solution thereto are often peculiar to the chemical and physical structure of the desired foamed product. In particular, the efficacy of the foam stabilizer is usually selective with respect to the formation of a particular type of foam. One factor to be considered in the evaluation of stabilizing efficacy is surfactant potency which is reflected by two types of measurements. One is the measured original height to which the foam rises as it is being formed. From this standpoint, the greater the foam rise, the more potent is the surfactant. The second potency measurement is concerned with the ability of the surfactant to maintain the original height of the foam once it has formed. Foams produced with surfactants which have good potency in this second respect undergo a minimum of settling or "top collapse" which may otherwise contribute to split formation and other foam defects.
The search for improved surfactants for stabilization of polyurethane foams is further complicated by the tendency of such foams to ignite readily and burn and the need to reduce their flammability. This characteristic is particularly objectionable in the case of flexible polyurethane foams in view of the use of such foams in many applications where fire is especially hazardous such as their use in automotive seat cushions and household furniture cushioning. One approach to reducing flammability of flexible foams is to include a flame-retarding agent such as various phosphorus and/or halogen-containing compounds as a component of the foam-producing reaction mixture. It is found, however, that surfactants which may otherwise be effective stabilizers of non flame-retarded as well as flame-retarded foam, may be deficient as stabilizers of flame-retarded foam in that they appear to have an adverse effect on the efficiency of the flame-retardant.
Among the various types of surfactants which have been used to advantage for stabilization of non flame-retarded flexible polyether-based urethane foams are polyoxyalkylene-polysiloxane block copolymers wherein silicon of the siloxane backbone is bonded only to methyl groups and the polyether portion of the polyoxyalkylene blocks is composed of oxyethylene and oxypropylene units. Such copolymers include those of both the hydrolyzable and non hydrolyzable types, that is, copolymers in which the polysiloxane and polyoxyalkylene blocks are linked through --Si--O--C-- and --Si--C-- bonds, respectively. From the standpoint of possessing a particularly good combination of potency and processing latitude in the stabilization of flexible polyether urethane foams, an especially useful class of non hydrolyzable block copolymers are those described in U.S. Pat. Re. No. 27,541. When used to stabilize polyether-based foams derived from reaction mixtures containing a flame-retardant, however, copolymers wherein the polysiloxane blocks are substituted only with methyl groups including copolymers of the hydrolyzable type, generally provide foams which either do not qualify as self-extinguishing (by flammability test ASTM D-1692-68), or, if so qualified, the burning extent of the foam is at a relatively high level, leaving room for further improvement in this regard.
It is desirable, therefore, and is a primary object of this invention, to provide a new class of polysiloxane-polyoxyalkylene block copolymers which, in addition to good potency as stabilizers of flexible polyether-based urethane foam, both non flame-retarded and flame-retarded, have the further advantageous property of allowing for the formation of flame-retarded foam of relatively low burning extent.
A further object is to provide particular flexible polyether urethane foam of substantially reduced combustibility and a method for the manufacture of such foam.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.
As a preface to the description of the present invention, it is noted that our U.S. Pat. No. 3,846,462 describes and claims a particular class of siloxane-polyoxyalkylene copolymers which possess the advantageous property of allowing for formation of flame-retarded polyether polyol-based urethane foam of relatively low burning extent. Among other characteristics, such copolymers comprise difunctional siloxy units in which the two organic radicals bonded to silicon are (1) alkyl and (2) either cyanoalkyl such as cyanopropyl [NC--C.sub.3 H.sub.6 --] or cyanoalkoxy such as cyanopropoxy [NC--C.sub.3 H.sub.6 O--] including combinations of these particular two types of silicon-bonded cyano-bearing groups. Our said patent, however, does not describe the particular class of novel copolymers to which the teachings of the present invention pertain.